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Why is My Check Engine Light On but no Codes

March 1, 2024 | Victor Lukasso

It can be a frustrating yet confusing situation when your check engine light is on, but the OBD-II scanner is detecting no Codes. If this is the case with you, you’ve found the perfect article for your needs.

Whenever the check engine light ignites on your car’s dashboard, it’s meant to warn you of troubles that need to be fixed on your vehicle. The PCM, ECM, and other computers on your car monitor and regulate the car’s emissions, fuel economy, and overall performance. The PCM stores a code in the vehicle’s computer memory when it detects a fault. This code can be retrieved using an onboard diagnostic scanner.

But do you know there could be times when your check engine light is on but no Codes will be detected on the OBD-II scanner? This is common, and several factors, such as a wrong/incompatible scanner, a blown fuse, user fault, wiring issues, and a contaminated port, can cause it.

In this article, we’ll further discuss why your check engine light will be on, but the scanner will read no Codes and how to fix the check engine light with no Codes.


Can a check engine light come on with no code?

Yes, a check engine light can come on with no code. While it’s less common, there are several reasons why this might happen. A loose or damaged gas cap, a blown fuse, a failing battery or alternator, and a glitch in the computer system are all potential causes.

It’s essential to close your gas cap tightly, replace a failing battery, and take the car to a mechanic if necessary to diagnose and resolve the issue.

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However, any reason other than the above implies that the diagnostic tool is outdated or you don’t know how to perform a scan properly.

Why is My Check Engine Light On but no Codes

Suppose your check engine light is on, but no Codes are being read on the OBD-II scanner. In that case, there’s a possibility that the OBD-II software isn’t compatible with your vehicle, or you don’t know how to set up the scanner correctly. Your car could have also suffered from a blown fuse, a wiring issue, or a dusty port, causing the scanner not to read the Codes stored on your computer correctly.

Here’s complete detail on how these factors could affect why your check engine light is on but no codes are detected.

Incompatible/Wrong Scanner

When you visit online stores or physical stores to purchase an onboard diagnostic scanner, you’ll be presented with different scanners from other producers. However, they claim to perform the same function.

If you purchase an older model or an OBD-II scanner produced in a foreign country, you’ll encounter issues while using it for diagnosis.

Codes won’t display on it even while your check engine light is on because your vehicle is a newer model and the software of the scanner is outdated and doesn’t currently support your vehicle, or the scanner isn’t compatible with the make or model of the car it’s being used on.

Also, when you go for free scans, the diagnostic tools used aren’t that premium, and they lack some Codes found in newer car models.

You can ask a mechanic to recommend the best diagnostic tools for your car or purchase from our recommended OBD-II scanners that work worldwide.

User Fault/Error

Most users mistake an OBD-II scanner for a simple DIY tool that connects it to the port and clicks on “read codes,” but there’s more to it.

Depending on the manufacturer, there might be some basic set-up that needs to be done that you might have skipped. Kindly revert to the buyer manual and follow the set-up process properly.

Here are some tips:

  • Ensure that the key is set to the ON position
  • Use an updated reader
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If it’s your first time using an OBD-II scanner, watch the video below to ensure you’re doing it right, or contact a professional mechanic for help.

Contaminated OBD Port

Dust or debris in the OBD connection port can cause the scanner to malfunction, thereby not detecting codes. This implies a contaminated port will cause the diagnostic tools not to create a connection with the computer.

In this case, you can inspect the connector and remove dust or other foreign particles. You can seek the help of a mechanic if you don’t know how to go about it.

A blown fuse

Electrical components of a car function properly because of the presence of a fuse; this includes the PCM, ECU, and ECM. If the fuse is blown, the check engine light will come up even if there’s no code recorded on the system.

The other problem with a blown fuse is that the computer might not record or display error codes on the dashboard.

In this case, you should call a mechanic to help you with the fuse replacement and check if the problem is resolved.

Electrical Short-Circuit

While an electrical short is unlikely to cause the trouble, it might still be responsible. This occurs when a connection of low resistance that allows damaging current flow through it is present in a circuit.

Let’s not diverge into electrical engineering, but you can easily decode this by turning the ignition key to the ON position without starting the engine. Usually, The light should go off after some minutes, but if the light remains on, then there’s a Short-Circuit.

How to Repair Check Engine Light On with No Codes

The first step towards resolving this is to ensure that the software installed on the OBD-II scanner supports your car’s make and model. You can confirm this by checking the buyer manual. If it doesn’t, you need to purchase a diagnostic tool of higher quality that’ll serve you.

Also, you might want to check if you’re using it appropriately by setting it up on another vehicle to see if it works. The directions on configuring it on your car should also be displayed in the buyer’s manual.

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In addition, check for any defects in the OBD Port and fix them as soon as possible because, without it, even an OBD scanner of higher quality won’t be able to connect with the computer.

If you know electrical components, you can check if the fuse that powers the ECM and PCM is not blown. You should take your vehicle to a professional mechanic for diagnosis and fixes.


Can you check engine light comes on and nothing be wrong?

No, whenever the check engine light comes on, it denotes a minor or major issue affecting the vehicle’s overall performance. You might not notice any change if it’s a minor issue, but significant problems often cause the car to stall, misfire, or turn off completely. You can use an OBD-II scanner to read the Codes.

Why is my check engine light on, but everything seems fine?

If your check engine light is on, but everything seems fine, then it’s because the problem is minor. Troubles such as a loose or damaged gas cap, faulty sensors, bad catalytic converter, etc., fall under this category.

Can a check engine light clear itself?

Yes, a check engine light will clear itself if you’ve fixed the trouble saved by the computer. Alternatively, you can manually remove and reinstate the battery to clear the codes or use an OBD-II scanner.

Can you turn off a check engine light without fixing the problem?

Turning off a check engine light without fixing the problem is impossible, but you can disconnect the system from showing any indication. However, remember that the fault that made the check engine light turn on is still present and can cause severe damage if not addressed.

Why won’t my scanner read codes?

If your scanner won’t read codes, the software doesn’t support the current model or make of the car you’re using it on. Also, as seen in the buyer’s guide, you may have forgotten to set the key to the ON position or other set-up guides.

Can you safely drive a car with the check engine light on?

Your ability to safely drive a car with the check engine light on depends on how severe the fault Is. Minor faults may not display any symptoms, but the major fault may result in an instant engine shutdown.

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Meet Victor Lukasso, the owner of V. Auto Basics. Through this blog, Victor Provides Insights on the latest tips, maintenance, repair, and techniques in the automotive world.